Multi-IDC support

[icycrystal4]

In many high availability scenarios, whole datacenter crash is supposed to happen any time. So many applications are build cross multiple IDCs, every single data center services a portion of traffics and accommodates the whole complete data. Every IDC will sync the traffic to the other data centers.
As a queue service, WQS should provide a abstract layer, so that the application developer programming cross multi-IDCs is as easy as single IDC.

1. producing a message is as fast as locally
2. consuming a message is as fast as locally
3. consuming latency is in a tolerable level
4. the throughput is as high as locally
5. the data stability is the same as locally